1. Field of the Invention
The present invention is directed to a method for confirming the effective dosage level of chlorine dioxide in a solution in the form of a wash, rinse, soak, paste, gel, aerosol spray, or other suitable delivery system while allowing differentiation of chlorine dioxide from ions that may interfere with the activation.
2. Description of Prior Art
Oral Disease
Oral disease refers to a number of generally preventable conditions of the mouth resulting from a variety of causes. Plaque is the most recognizable precursor to oral disease. It is the biofilm that forms on teeth within hours after they are cleaned. The main mineral component of teeth is hydroxyapatite (HAP) and when teeth are cleaned, HAP becomes exposed to the oral environment. Salivary proteins such as mucins, proline-rich proteins, statherins, histatins, and cystatins have a strong affinity for HAP. These proteins quickly bind or adsorb to the exposed HAP of the tooth to form a thin coating called the acquired pellicle. Certain bacteria in the oral cavity selectively adhere to the pellicle, begin to divide, and form colonies. Initially, approximately 80% of the bacteria that colonize pellicle-coated tooth surfaces are facultative, gram-positive, non-motile cocci such as Streptococcus sanguinis (formerly Streptococcus sanguis). The other 20% include a variety of gram-negative bacteria such as Veillonella species. As the colonies grow, the environment changes due to the metabolic activities of these early colonizers and the addition of diverse groups of other bacteria to the biofilm (plaque) mass.
An important environmental change in the plaque biofilm is the lowering of the local oxidation-reduction potential thus creating a low-oxygen environment that promotes the colonization and growth of anaerobic bacteria. Microorganisms in the biofilm synthesize a slime matrix or glycocalyx from the abundant polysaccharides, glycoproteins, and dietary sugars (e.g., sucrose) present in the oral environment. Eventually, the plaque becomes a characteristic biofilm with a highly structured, matrix-embedded, diverse microbial population in which gene expression is severely altered.
The volume and structure of the biofilm created provides protection to the bacteria housed within it, potentially reducing the efficacy of antimicrobials. As a result, disruption of the biofilm of plaque is typically accomplished by mechanical means (e.g., brushing, flossing, professional tooth cleaning). Use of certain anti-plaque and antiseptic agents has been suggested for prevention of biofilms, but these treatments are typically tested in vitro using pure strains of microbes cultured on agar. Such in vitro conditions do not adequately simulate the biofilm environment, which may limit the significance of the test results.
Within biofilms, continuous metabolic activity of bacteria produces acids that can demineralize tooth enamel and dentin leading to the development of dental caries and progressive tooth decay. This demineralization is irreversible unless there is early intervention by a dental professional who might recommend the inclusion of certain fluoride-containing oral care products in the daily dental routine. If left untouched, demineralization can progress to the inner layers of the tooth, leading to severe pain and increased potential for loss of the tooth.
If dental plaque is left undisturbed, deeper portions of the plaque biofilm mineralize leading to the formation of calculus. Calculus has two major components, organic material and inorganic material. The organic portion of calculus consists mainly of dead bacteria. The inorganic part of calculus is composed of several minerals derived from calcium and phosphate present in the oral environment. There are two types of calculus, subgingival (below the gum line) and supragingival (above the gum line). Supragingival calculus is highly organized, porous, and visible. Once formed, calculus cannot be removed by conventional brushing and flossing; the intervention of a dental professional is generally required. Calculus retention is problematic for oral health because it harbors biofilm-forming bacteria that can lead to the development of periodontal (gum) infections.
Halitosis (bad breath) is caused primarily by the presence of volatile sulfur compounds (VSCs) in expired breath. Approximately 90% of foul odors in expired mouth air are due to the presence of the two major VSCs: hydrogen sulfide (H2S) and methyl mercaptan (CH3SH—also called methanethiol). The sulfur in these VSCs comes from the breakdown by bacteria of sulfur-containing proteins from saliva, plaque, and sloughed epithelial cells. Increased production or build-up of any of the protein sources will lead to higher levels of VSCs in mouth air.
There are a number of known situations that will lead to increased VSC production. For example, persons who do not perform adequate oral hygiene will have abundant amounts of supragingival and subgingival plaque biofilms on their teeth. This is especially true in difficult-to-clean locations such as interproximal areas between the teeth. In addition, natural teeth that support some dental prostheses are difficult to clean. Finally, the dorsal surface of the tongue is rough, irregular, and harbors large quantities of microorganisms. In general, the microorganisms in chronic intraoral biofilms will produce large quantities of VSCs. Besides being the major contributor to halitosis, VSCs are potent irritants and can aggravate existing inflammation of the gums. High levels of VSCs can kill epithelial cells that may lead to increased permeability and ulceration of the gum tissue. The existence of open wounds coupled with increased gum tissue permeability can promote the entry of bacteria into the bloodstream (i.e., bacteremia). Chronic bacteremia may increase the risk for the development of a number of systemic problems such as heart attacks, stroke, and adverse birth outcomes.
Gingivitis is defined as the presence of gingival inflammation without loss of connective tissue attachment. The precursor to gingivitis is undisturbed dental plaque biofilms. Studies have shown that gingivitis will develop within 10-21 days if all oral hygiene practices are stopped and plaque is allowed to accumulate undisturbed. Clinical signs of gingivitis are redness, swelling (edema), and bleeding gums.
Periodontitis refers to a group of infections in which the supporting tissues of the teeth such as connective tissue and bone are destroyed by plaque-induced inflammation. The most common form is known as Chronic Periodontitis that affects approximately 20% of the adult U.S. population. Signs of chronic periodontitis include all of those associated with gingivitis (i.e., redness, swelling, bleeding) plus the formation of deep periodontal pockets (increased probing depths), gingival recession, increased tooth mobility, and loss of bone as detected by radiographs. If left untreated, chronic periodontitis can lead to tooth loss. Chronic periodontitis is a multifactorial disease in which host susceptibility to infections and multiple groups of bacteria are etiologically important. Factors that increase susceptibility to intraoral infections such as poor oral hygiene, smoking, diabetes mellitus, emotional stress, and innate (genetic) host responses to bacterial challenges also increase the risk of developing chronic periodontitis. Several dozen types of oral bacteria have been implicated as putative periodontal pathogens including gram-negative bacteria such as: Porphyromonas gingibalis, Aggregatibacter actinomycetemcomitans, Tannerella forsythia, Eikenella corrodens, Prevotella intermedia, and Campylobacter rectus. Gram-positive bacteria of importance include Streptococcus intermedius, Micromonas micros, and Eubacterium species. Spirochetes such as Treponema denticola are also important. Low levels of most of these pathogens can be isolated from healthy mouths. These bacteria only become a problem when they are left undisturbed in mature dental plaque biofilms. Finally, chronic periodontitis is a polymicrobial infection with multiple bacteria working together in a biofilm to cause the disease.
Treatment of both gingivitis and chronic periodontitis is designed to facilitate the frequent removal and disruption of dental plaque biofilms. For gingivitis, effective oral hygiene practices on a daily basis are usually sufficient. This involves thorough removal of plaque from facial and lingual surfaces of the teeth with a toothbrush and good interproximal care with dental floss or other appropriate devices (e.g., toothpicks). Periodic tooth cleaning by an oral health care provider is required to remove mineralized plaque (i.e., calculus). Treatment of chronic periodontitis is more difficult since the disease-causing plaque is usually at subgingival sites and in deep periodontal pockets. Standard interventions usually include oral hygiene instructions followed by thorough subgingival debridement (i.e., scaling and root planing). If the infection persists, surgical intervention may be recommended to reduce the depth of the pockets and to gain access to thoroughly remove the calculus deposits on root surfaces. In some cases, reconstructive surgical procedures are performed in an attempt to regain some of the lost periodontal attachment and supporting bone. Once the infection is under control, the patient is placed on a rigorous maintenance/recall program to reduce the chances of recurrent infection. It is during this maintenance phase of therapy that non-invasive over-the-counter products are especially useful in slowing down the reformation of dental plaque biofilms on tooth surfaces. Current over-the-counter anti-plaque and anti-gingivitis products do not meet all of the needs of consumers. On the other hand, prescription mouth rinses such as those containing chlorhexidine gluconate are effective treatments for gingivitis, but are not intended for long-term use, may stain teeth, and have an unpleasant taste. An example of a non-prescription mouth rinse sold under the trademark is Listerine®, which has been granted the ADA seal of approval as an anti-plaque and anti-gingivitis product. However, the high alcohol content and harsh taste of the formulation can be unpleasant for some consumers.
The use of chlorine dioxide for sanitation was first suggested in 1948 by Eric Woodward to reduce the incidence of unpleasant taste in shrimp. Since then, chlorine dioxide use has spread into a number of other industries. The oxidative power of ClO2 is used in the manufacturing of wood pulp as an agent for the bleaching of cellulose fibers. In water treatment, ClO2 has become widely used for water sanitation. It has been shown to be effective at reducing the bacterial content, algae content, and odor associated with wastewater treatment. Additionally, the utilization of ClO2 for treating drinking water has been effective without adversely affecting its taste. The benefits of ClO2 over other processes utilizing ozone or bleach for example, are reduced cost, reduced toxicity and reduced production of chlorinated by-products.
In 1999 the EPA published “Alternative Disinfectants and Oxidants Guidance Manual,” describing disinfectant uses for ClO2 and containing information on the mechanism of generation, application and standards and regulations governing use of ClO2 and other disinfectants. Major applications listed by table 4-5, section 4.8.2 in the manual are as follows: primary or secondary disinfectant, taste control, odor control, TTHM/HAA reduction (total trihalomethanes are chlorinated organics, chloroform [CHCl3] and dichlorobromomethane [CHCl2Br] for example; haloacetic acids are created when an atom from the halogen group, chlorine, for example, replaces a hydrogen on the acetic acid molecule), Fe and Mn control, color removal, sulfide destruction, phenol destruction and Zebra mussel control [EPA 1999, p. 4-34]. These are accomplished by oxidation of various substances found in water. For example, unpleasant tastes and odors (sulfides, phenols, others) can exist in water due to vegetative decay and algae content. ClO2 reduces these tastes either by eliminating the source (algae) or oxidizing the causative taste and odor molecules. In the control of iron and manganese, ClO2 will bring the dissolved ions out of solution to form precipitates, which may be eliminated through filtration and/or sedimentation. Zebra mussel control is important because it helps to maintain the natural ecology of a body of water. Zebra mussels are organisms that will infest a lake or river, strip it of nutrients and create a pseudo-fecal mucous layer on the bottom. The use of ClO2 for water sanitation and pulp treatment generally involves on-site generation followed by immediate use.
The term ‘stabilized chlorine dioxide’ on the other hand, refers to the generation and subsequent sequestration of ClO2, which allows for its storage and availability for later use. The first reference to stabilized chlorine dioxide in patent was in U.S. Pat. No. 2,482,891 in which ClO2 is stabilized in a powder for storage. For its application, it is mixed with water to “liberate” the chlorine dioxide. A method and composition for the use of aqueous stabilized chlorine dioxide for antiseptic purposes was noted in U.S. Pat. No. 3,271,242. The 1979 text Chlorine Dioxide, Chemistry and Environmental Impact of Oxychlorine Compounds, describes (aqueous) stabilized chlorine dioxide as follows:                “The stabilization of chlorine dioxide in aqueous solution was proposed by using perborates and percarbonates. Thus, a stabilized solution of ClO2 would be obtained at pH 6 to 8 by passing gaseous ClO2 into an aqueous solution containing 12% Na2CO3.3H2O2. Other variants are possible. In reality, it seems that in these methods, the chlorine dioxide is practically completely transformed to chlorite. Dioxide is released upon acidification . . . ” [Masschelein, 1979]The reference to percarbonates and perborates may be replaced by the term ‘peroxy compounds,’ which would refer to any buffer suitable for maintaining the pH and hence, the stability of the ClO2 in solution. The buffer is a necessary component, as the ClO2 is unstable at low pH. Once the solution reaches low pH or encounters an area of low pH, the stabilized ClO2 is released from solution and available for sanitation and oxidation.        
In oral care products, the use of stabilized ClO2 has been suggested as an active ingredient by a number of patents: U.S. Pat. Nos. 4,689,215; 4,696,811; 4,786,492; 4,788,053; 4,792,442; 4,793,989; 4,808,389; 4,818,519; 4,837,009; 4,851,213; 4,855,135; 4,886,657; 4,889,714; 4,925,656; 4,975,285; 5,200,171; 5,348,734; 5,489,435; 5,618,550. Additionally, the use of stabilized ClO2 has been suggested for the degradation of amino acids in U.S. Pat. No. 6,136,348. The premise for these products is that the stabilized chlorine dioxide will remain as such until it encounters the localized reductions in pH. Reduced pH levels can be a result of low pH saliva or oral mucosa, the accumulation of oral disease-causing bacteria or the presence of plaque biofilms on teeth and epithelial cells. Once released, the now active chlorine dioxide is effective at killing bacteria and oxidizing VSCs. Data have shown dramatic reduction in bacteria after exposures as short as 10 seconds, as set forth in U.S. Pat. No. 4,689,215. Additional data show remarkable decrease in VSCs in expired mouth air; the mechanism is believed to be oxidation of VSCs through the cleavage of the sulfide bonds.
The effectiveness of the chlorine dioxide is likely dependent on the amount of ClO2 released from stabilized chlorine dioxide when the solution is acidified. The amount of ClO2 released depends on the initial concentration of the solution, its pH, and the stabilizing buffer or agent used. It could follow that that the efficacy of the chlorine dioxide as an oral care product is dependent on the amount of ClO2 released from the stabilized chlorine dioxide solution. As a result, it is imperative that accurate, precise measurements are taken so the concentration of stabilized ClO2 and of the release of ClO2 from solution can be determined. In addition to the need to quantify the efficacy of the solution, concentrations must be understood to ensure the safety of the product.
A concern about the stability of stabilized ClO2 was recited in U.S. Pat. No. 5,738,840 with reference to the inclusion of “other oxychlorine species” which could refer to chloride [Cl−] or chlorate [ClO3−]. The mechanism of action was questioned and suggested that at pH between 6.2 and 7.0 “any molecular chlorine dioxide which forms by degradation of the chlorite is converted back to chlorite by reaction with the residual stabilizer.” This reverse reaction is unlikely due to the lower pH in the bacteria-laden target areas of the mouth described earlier. U.S. Pa. No. 6,231,830 calls into question the stoichiometry and safety of the formulation presented in U.S. Pat. No. 5,738,840. It is claimed that the formulation described is a ‘chlorinator’ in which “ . . . a build-up of chlorate ion, an unwanted by-product” may occur.
The analytical methods for measurement recited in U.S. Pat. Nos. 5,738,840 and 6,231,830 are important to note. In the patent '840, the concentration was determined using spectrophotometry. No reference was made as to the use of a chemical indicator such as Chorophenol Red, as is used in typical analytical tests for chlorine dioxide content. The wavelength used was 360 nm, which is in the ultraviolet part of the electromagnetic spectrum. The only type of measurement in the patent '830 seemed to be a visual observation of brown tint from free iodine in samples. Neither method provided sufficient means to determine the dosage of active ingredient and the dosage of undesirable and potentially dangerous chlorates and chlorides.